1. Field of the Invention
The present invention relates to a new modulation scheme, for use in digital communications called "pulse to zero" (PZ) modulation. A novel receiver and demodulator, useful in detecting and decoding the pulse to zero (PZ) modulation, is also disclosed. Since the receiver requires neither a local power supply or clock, it is uniquely suited for use in medical implants.
2. Description of the Prior Art
Various modulation schemes are known for transmitting pulsed digital communications. Generally either the frequency, amplitude, phase and/or spacing of pulses are modulated in such a manner as to convey useful information.
One such modulation scheme known in the art is pulse position modulation (PPM). In this scheme, the intelligence is contained in the spacing (or time lapsed) between two pulses. Generally, the spacing between a gate pulse and a signal pulse is measured. The following U.S. Pat Nos. teach this modulation scheme: 2,421,022; 2,521,710; 2,837,644; 2,894,127; 3,138,759 and 4,059,806.
Other modulation schemes using pulse spacing or timing are also taught. U.S. Pat. No. 3,209,259 issued to Huber describes a monocycle position modulation scheme in which the position of a single sine wave, within a time period conveys useful information. U.S. Pat. No. 3,713,140 issued to Meslener describes a decoder in which a transition occurring at the middle of a bit cell indicates a "1" and a transition occurring at the partition between adjacent bit cells indicates a "0". U.S. Pat. No. 3,537,100 issued to Barjot et al describes a non-return-to-zero (NRZ) code demodulation that decodes a "0" if the number of transitions in a time window are less than a given value and when the number of transitions are greater than the given value. All the above references teach a modulation scheme that first conveys time window information and then "looks" for the occurrence of recognizable event within the time frame.